The present invention relates to the field of diverters used in marine seismic operations. More particularly, the invention relates to an expandable diverter useful in marine seismic operations which can be expanded or retracted to adjust the storage volume and performance characteristics of the diverter.
Marine seismic diverters control movement of seismic streamers and other equipment relative to a seismic tow vessel. As the tow vessel moves through the water, one or more streamers or other equipment carrying cables are towed at a known velocity through the water. For a single cable, a diverter can control movement of the cable tail end in cross currents and in tow vessel turns. For multiple cables, diverters pull the cables outwardly from the vessel centerline to establish and to maintain selected cross-line cable spacing and placement in a seismic array. Diverters are also used to control the elevation of the diverter and other seismic equipment in the water.
Marine seismic diverters typically have fins or wings for urging the diverter and attached cable away from the seismic array centerline, or to control the diverter elevation. The displacement forces exerted by the diverters depend on the tow vessel speed, the diverter shape, and the diverter surface area in contact with the water.
The diverters are typically stored on board a seismic vessel for transport to the survey site. Diverters are bulky and require significant storage space during such transport. Diverters can be stored in pieces or sections for assembly at the survey site, however such systems are time consuming and are not adjustable when the diverter is positioned in the water. When the survey site is reached, the diverters and other seismic equipment are removed from the storage areas and are deployed into the water. U.S. Pat. No. 4,313,392 to Guenther et al. (1982) disclosed a system for deploying and retrieving seismic source assemblies.
Various deflecters such as paravanes and other devices have been developed for marine seismic operations. U.S. Pat. No. 3,611,975 to Ashbrook (1971) disclosed a paravane having wing members for controlling the paravane elevation. U.S. Pat. No. 3,774,570 to Pearson (1973) disclosed a paravane having pivoting diving planes for controlling the paravane elevation. U.S. Pat. No. 4,033,278 to Waters (1977) disclosed cable paravanes having adjustable hydrofoil and stabilizer elements. U.S. Pat. No. 4,323,989 to Huckabee et al. (1982) disclosed steering devices for maintaining a float in a desired lateral position. U.S. Pat. No. 4,484,534 to Thillaye du Boullay (1984) disclosed a profiled wing having profiled caissons at the lateral end, together with a central rib. U.S. Pat. No. 4,676,183 to Conboy (1987) disclosed a submersible positioning device having stabilizers for controlling movement of the device.
Other diverter systems have been developed. U.S. Pat. No. 4,719,987 to George et al. (1988) disclosed a bipolar paravane having left and right wings for providing a side force in the water. U.S. Pat. No. 4,890,568 to Dolengowski (1990) disclosed a tail buoy controllable with rudders. U.S. Pat. No. 5,357,892 to Vatne et al. (1994) disclosed a diverter having a lever for adjusting the streamer attachment point. U.S. Pat. No. 5,532,975 to Elholm (1996) disclosed a positioning device having wings and rudders for controlling movement of the device through water.
Conventional diverters use wings, moving planes, and rudders to control movement of the diverters through water. The effectiveness of such mechanical controls depends on numerous factors including the wing size, tow speed, and other considerations. The size of conventional diverters increases as the width and length of seismic arrays increases, thereby requiring more transport space and handling requirements. Significant cargo space is required for diverter handling, therfore adding to the overall vessel size requirements. Accordingly, a need exists for an improved diverter which is easy to handle and provides enhanced diversion capabilities.